Several methods are known for obtaining polysuccinimide, which when hydrolyzed to form the corresponding poly(amino acid) is useful as an absorbent, hard-surface cleaner, water-treatment additive for boiler waters and cooling towers and as a detergent additive acting as a builder, anti-filming agent, dispersant, sequestering agent and encrustation inhibitor. However, all of the previously known methods for preparing polysuccinimide suffer from the drawbacks of excessively long process times, expensive starting materials, or require the handling of solid materials which poses many difficulties in a manufacturing environment.
U.S. Pat. No. 5,057,597 to Koskan discloses a solid-phase process for preparing polysuccinimide by fluidizing an amino acid with agitation in a nitrogen atmosphere at a temperature of at least 180.degree. C. for three to six hours. The resultant polysuccinimide is then hydrolyzed to form a poly(amino acid).
U.S. Pat. No. 4,839,461 to Boehmke, et al. discloses a process for preparing poly(aspartic acid) by combining maleic acid or maleic anhydride and an ammonia solution in a molar ratio of 1:1-1.5. The mixture is then heated to 120.degree.-150.degree. C. and the resulting solution of ammonium salt and maleic acid is evaporated, leaving a crystal mash. The crystal mash is then melted, during which time the waters of condensation and crystallization distill off. A porous mass of poly(aspartic acid) results. The entire process requires six to eight hours to complete.
Japanese Patent 52-0088773 B assigned to Ajinomoto, discloses a solvent-based process for the preparing poly(aspartic acid). The process described therein utilizes a hydrohalic acid salt of aspartic acid anhydride in one or more organic solvents. The solvents disclosed are organic acids such as propionic acid, butyric acid, and valeric acid; alcohols such as tert-butyl alcohol and tert-amyl alcohol, esters such as ethyl acetate and butyl acetate; ketones such as methyl isobutyl ketone and cyclohexanol; ethers such as tetrahydrofuran and dioxane; halogenated hydrocarbons such as ethylene dichloride and dichlorobenzene; hydrocarbons such as toluene, xylene and decalin; and amides such as dimethylformamide. These solvents may impart additional hazards, expense, odor, toxicity and removal steps to obtain the final product.
The prior art methods for the synthesis of polysuccinimides and poly(amino acids) are time consuming, complex or use large volumes of volatile organic solvents or inert gases. As used hereinafter and in the appended claims, "polysuccinimides" refers to polymeric materials which contain succinimide moieties in the polymer chain and may contain other moieties, and "polysuccinimide" refers to polymeric materials which contain only such moieties.
It is an object of the present invention to provide a solvent process for producing polysuccinimides.
It is a further object of the present invention to provide a solvent process for producing polysuccinimides which does not require a product separation step.